Study On Biochemical Treatment Of Pyridine Carboxylic Acid Wastewater

Pyridine carboxylic acids,with special structure and many special pharmacodynamics,are indispensable raw materials and intermediates in pesticide production.Because of its stable structure,difficult biochemical degradation and certain toxicity,the wastewater produced in its production and use process is extremely difficult to treat.At present,there are few studies on this kind of wastewater,and biochemical method with the characteristics of large capacity and low cost is the main direction of studying to treat this kind of sewage.In this paper,the typical 3,6-dichloropyridine-2-carboxylic acid?dichloropyridinic acid?,3,4,5,6-tetrachloropyridine-2-carboxylicacid?tetrachloropyridinicacid?,4-amino-3,5,6-trichloropyridine-2-carboxylic acid?aminopyridinic acid?are studied in biochemical degradation.Firstly,the influencing factors of dichloropyridinic acid,tetrachloropyridinic acid and aminopyridinic acid wastewater in microorganisms were studied,it was found that the removal rate of the three acids was the best when the temperature of anaerobic,facultative and aerobic ponds was 35?,the pH value of anaerobic and facultative ponds was 7-7.5,the pH value of anaerobic ponds was 6-9,the dissolved oxygen content was 3-5 mg/L and COD/NO₃^--N was 15 in facultative ponds.Secondly,the kinetics types of dichloropyridinic acid,tetrachloropyridinic acid and aminopyridinic acid wastewater in anaerobic,facultative and aerobic tanks were investigated,and the microbial degradation rates of the three acids were analyzed.It was found that the removal rates of three acids in anaerobic,facultative and aerobic tanks decreased with the increase of concentration when the concentration was less than 250 mg/L;in anaerobic tanks,the degradation of three acids accorded with the first-order degradation kinetics;in facultative and aerobic tanks,the degradation of three acids accorded with the zero-order degradation kinetics;the order of the biodegradability of three acids was aminopyridine carboxylic acid>dichloropyridine methyl.Acids>tetrachloropyridinic carboxylic acid.Then,the mutual inhibition of three acids was studied.It was found that the addition of two other acids in dichloropyridinic acid,tetrachloropyridinic acid and aminochloropyridinic acid could strongly inhibit the substrate acid.In addition,the effects of several simple co-metabolites on microbial degradation of three acids were explored.In anaerobic and facultative ponds,the order of the effect of co-metabolic substrates on the removal rates of three acids was:glucose>sucrose>starch>methanol.In aerobic ponds,the order of the effect of co-metabolic substrates on the removal rates of three acids was:sucrose>glucose>starch>methanol;when the ratio of glucose concentration to substrate concentration was 8:1,the removal rates of raw substrates were Maximum.Finally,the removal efficiency of the three acids was tested by A₂O process.During the load stabilization period,the COD removal rate decreased with the increase of influent concentration.After adding glucose,the total COD removal rate of A₂O process increases.When the influent concentration was 50 mg/L,100 mg/L,150 mg/L,200 mg/L and 250 mg/L,the total removal rate of COD increased by 5%,5.5%,6.7%,6.2%,5.6%when the influent was dichloropyridinic acid,4%,5.9%,6.5%,6.2%,5.2%when the influent was tetrachloropyridinic acid,and 2.8%,5.9%,5.3%,6.1%,6.7%when the influent was amlopyridinic acid.